The immediate objective of this research is to modify the life-span of rats by dietary manipulation in order to aid in the identification of causal metabolic changes involved in the senescence of skeletal muscle and of the whole organism. Studies will be conducted on this organ in the "resting" state and following pertubation by stressful stimulus. Rats will be exposed to two life-long nutritional regimes from weaning; ad libitum feeding ("over feeding") or moderate total food restriction. Detailed studies of the biochemical pathology of aging in skeletal muscle will be accomplished by use of cell-free systems in order to determine the functional status of muscle ribosomes and other components of the protein synthetic apparatus. In addition, methods will be explored to determine the effects of nutritional status and progressive aging as the initiation and elongation rates of muscle protein synthesis and as the level of translatable myosin on RNA. The long term objective of this work is to define the intimate biochemical processes involved is the loss of muscle mass and bodily function as the organism ages.